This application is based on French Patent Application No. 01 02 074 filed Feb. 15, 2001, the disclosure of which is hereby incorporated by reference thereto in its entirety, and the priority of which is hereby claimed under 35 U.S.C. xc2xa7119.
1. Field of the Invention
The invention relates to a method of storing data resulting from the operation of a data processing system and stored in storage means of the system, referred to herein as main storage means, and which is copied (to provide a xe2x80x9cback-upxe2x80x9d for use in an emergency) in storage means, referred to herein as auxiliary storage means, so that the data can be copied back in the event of an incident preventing use of data stored in the main storage means. The invention also relates to a storage device for implementing the method.
2. Description of the Prior Art
Computer data is routinely backed up on a storage medium other than that on which the data is initially stored to limit the inconvenience resulting from loss of data from a data processing system, which can have diverse causes, such as a hardware fault or software error, for example, or an operator error.
One prior art method periodically performs two separate back-ups in a data processing system. A first periodic back-up makes a complete copy onto a particular media module of all of the files containing data resulting from the operation of the data processing system over a period of time that can be considered to constitute a long period, for example one or two weeks. The second periodic back-up makes a selective and incremental copy of files containing data resulting from the operation of the data processing system over a much shorter period of time, for example of the order of one day. Thus an incremental back-up copies only files created or modified since the immediately preceding back-up.
The volume of data to be copied in a complete back-up and the duration of that operation usually prevent repeated back-ups at frequent intervals, in particular if the data processing system includes a large number of interconnected machines.
A drawback of the prior art method described above is that it is not easy to restore lost data from copies made by the periodic back-up operations that it provides if the restore operation must take into account a plurality of copies, for example a series of copies spanning a period of more than a few weeks. The operations to be carried out to restore the data then become very complex, and can therefore entail reading a relatively large number of media modules, and take too long to provide a satisfactory response to the needs of users, on whose behalf the data processing system is operated, since the fastest possible restoration of the data is generally required. The benefit of an incremental back-up is that it makes it possible to supply each user with a copy of the work that they were doing in the state at which that work existed at the time of the back-up, short of always being able to restore the work to the user in the state in which it existed at the time it was unintentionally interrupted. The objective aimed at is to avoid each user having to redo, or have redone, work that has been done and unintentionally interrupted, and delayed restoration of data rapidly becomes of no benefit in the case of work in progress.
The invention therefore proposes a method of storing data processed during the operation of a data processing system, stored in the form of files in main storage means of the system and backed up by copying it to auxiliary storage means, which method includes, at transfer initiation times periodically recurring with a long period, transferring files stored in the main storage means of the system when it is operating from the primary storage area in which they are initially stored in the main storage means to a secondary storage area of the main storage means if they have not been created and/or modified during the immediately preceding long period, in order to separate files recently created or modified from other files, to enable differentiated back-ups.
According to the invention files stored in the primary storage area are backed up by complete copying to the auxiliary storage means of the system at an intermediate period less than the long period, of which it is preferably a submultiple, and by incremental copying to the auxiliary means at a short period less than the intermediate period, of which it is preferably a submultiple, files stored in the secondary storage area being backed up to the auxiliary storage means with the long period.
According to the invention, files are periodically transferred from the primary storage area to the secondary storage area in the main storage means under the control of the operating system of the data processing system including the main storage means and in a manner that is entirely transparent to a user.
According to the invention, access pointers to files stored in the secondary storage area of the main storage means are stored in a database located in a primary storage area of the main storage means that is updated on transferring files from the primary storage area to the secondary storage area and in the event of requests to modify or eliminate a file stored in the secondary storage area, each request leading to the deletion of the pointer for accessing the file in the secondary storage area after copying the file into the primary storage area in the case of a request for modification.
The invention also proposes a data storage device for a data processing system including storage means for storing data assigned to a data processor entity that includes at least one processor and operates in conjunction with a clock system, the storage means including:
main storage means in which the data is stored in the form of files and with which at least one processor of the processing entity communicates for transmission and command purposes when the data processing system is operating, and
auxiliary back-up storage means for storing files periodically copied from the main storage means.
According to the invention, the main storage means are organized into at least two separate storage areas, including a primary area for storing files newly created and/or modified and a secondary area into which are periodically transferred, at a transfer initiating time recurring periodically with a specified long period, files stored in the primary area that have not been created and/or modified during the immediately preceding long period, the areas providing for differentiated back-ups of files recently created or modified and other files, producing copies of different files at different periods.
The invention, its features and its advantages are explained in the following description, which is given with reference to the single FIGURE of the accompanying drawing.